1. Field of the Invention
The invention generally relates to automatically reassigning an interface card and devices between operating environments, and more particularly, to automatically reassigning interface cards and devices in a programmable logic controller system from a non-deterministic operating environment to a deterministic operating environment.
2. Background Description
Programmable Logic Controllers (PLCs) typically include a customized piece of hardware that has an instruction set geared for the industrial control 5 industry. This piece of hardware is often referred to as a Hard PLC. The programming language is usually ladder logic or some other language that typically resembles assembly language. The programs (control programs) usually involve the manipulation of memory areas in the PLC that are tied through other specialized pieces of hardware (I/O modules) to machinery such as, for example, switches, pumps, motors, machines, etc. These I/O modules are usually mounted on a rack and can be accessed over a network.
In recent years, the control industry has expanded to take advantage of the power of the Personal Computer (PC). A Soft PLC is a software version of the Hard PLC. Instead of having actual circuitry boards that execute the control program, a software program that runs on the PC executes the program. Additional cards can be inserted into the PC chassis to allow for access to the I/O modules. The Soft PLC will interface with these cards which in turn interface with the I/O modules.
There is another version of the PLC called a Slot PLC. This is a piece of hardware which is in the form of a card that can be inserted into the PC's chassis. The Slot PC behaves like a Hard PLC and has a limited amount of accessibility to other applications on the PC.
Typically, an operating system such as, for example, Windows® (Windows® is a registered trademark of Microsoft Corporation) is used as the environment for the PLC application software to run under and interact with the I/O devices. This environment is a non-deterministic environment and essentially non-real time. However, over time, as the devices or operational requirements of the equipment being controlled changes, the demands on the operating system may become overtaxed and often cannot meet more demanding real-time constraints for new equipment or new requirements for the equipment being controlled. Often this may be simply due to more equipment, for example, on the PLC I/O interfaces vying for more application processing time.